Australian police have arrested IT security professional and self-proclaimed leader of an international hacking ring Matthew Flannery after he allegedly infiltrated a government website this month.

The 24-year-old man, from Point Clare on the NSW central coast, claims to be a leader of the international hacking group LulzSec.

LulzSec, an abbreviation of ''lulz'' (laughs) and security, was formed in 2011. The group has claimed responsibility for multiple high-profile cyber attacks, including against Sony, Rupert Murdoch's News International, the CIA and other government organisations. They are also associated with prominent international hacking group Anonymous.

Flannery, known online as Aush0k, is a "well-informed" IT professional who worked for Sydney-based firm Content Security. The company said he was a recent hire and has been dismissed since being arrested on Tuesday evening, and no longer has access to Content Security's building or computer system.